1. Field of the Invention
The present invention is generally related to a trim tab for use in a jet propulsion system and, more particularly, to a trim tab that is attached to the inner cylindrical surface of a nozzle of the jet propulsion system.
2. Description of the Prior Art
Trim tabs have been known for use in outboard motor and stern drive types of marine propulsion systems for many years. The primary function of a trim tab is to provide a minor adjustment to the steering alignment of a marine propulsion system which is intended to eliminate lateral forces on a watercraft during normal operation.
U.S. Pat. No. 3,955,527 which issued to Holtermann on May 11, 1976, describes a marine propulsion trim tab with an anti-ventilation device. A marine propulsion device includes a lower unit that comprises a laterally extending anti-cavitation plate extending from the lower unit above a propeller and including a trailing portion, together with a trim tab extending downwardly from the trailing portion of the anti-cavitation plate aft of the propeller. It also comprises a deflector that is located aft of the propeller and extending from the trailing portion from the anti-cavitation plate and rearwardly of the trim tab for pressurizing the water forward thereof and below the anti-cavitation plate and in the region of the trim tab during forward movement of the lower unit through the water.
U.S. Pat. No. 3,817,202 which issued to Holtermann on Jun. 18, 1974, describes an anti-ventilation fence for a trim tab. A stern drive unit includes a trim tab extending from a driveshaft housing behind a propeller and downwardly into an imaginary cylinder projecting rearwardly in concentric relation to the propeller axis from the top of the tip of the propeller, and a generally horizontally projecting barrier extending from the trim tab and located below the intersection of the imaginary cylinder and the trim tab.
U.S. Pat. No. 3,799,103, which issued to Granholm on Mar. 26, 1974, describes a stern drive unit trim tab. The stern drive lower unit comprises a lower portion which is at least partially submerged during normal operation and which includes a rotatably mounted propeller shaft carrying a propeller, and a trim tab which is located rearwardly and above the propeller and which includes two side surfaces, one of which is subject to thrust or impact by water propelled by the propeller and is provided with a forward portion and a rearward portion offset from the forward portion in the direction toward the other of the side surfaces.
U.S. Pat. No. 4,908,766, which issued to Takeuchi on Mar. 13, 1990, describes a trim tab actuator for an propulsion device. The improved trim tab actuator for a watercraft is intended for use in permitting the operator to automatically select any of a plurality of steering effects by automatic control of the trim tab. The trim tab is positioned in response to sense steering and watercraft conditions and the operator may also select any of a plurality of modes mapped in response to these conditions.
U.S. Pat. No. 4,509,924, which issued to Hall on Apr. 9, 1985, describes a control system for a torque correcting device. The invention provides a marine propulsion device comprising a propulsion unit, a transom bracket adapted to be fixedly connected to a boat transom and a swivel bracket mounted on the transom bracket for pivotal movement about an axis which is horizontal when the transom bracket is boat mounted. The marine propulsion device also includes a king pin assembly mounted on the swivel bracket for pivotal steering movement of the propulsion unit and a mounting mechanism for mounting the propulsion unit on the king pin assembly and permitting limited rotational movement of the propulsion unit relative to the king pin assembly. The marine propulsion device also includes a trim tab mounted on the propulsion unit for pivotal movement about an axis transverse to the horizontal axis, and a linkage mechanism for displacing the trim tab about the transverse axis in response to rotational movement of the propulsion unit relative to the king pin assembly.
U.S. Pat. No. 4,693,689, which issued to Harada on Sep. 15, 1987, describes a controlling gear for an outboard engine. The outboard motor embodying an improved throttle and trim tab control mechanism comprised a trim tab which is pivotally supported by the outboard motor for assisting in its steering operation. The trim tab is operated by means of a pair of flexible transmitters that are fixed, at their upper ends, to extend in a generally longitudinal direction and which are operated from a drum by means of lost motion connection that is operative in response to movement of the steering lever relative to the outboard motor. The steering lever is further supported for rotation and is operatively connected to the engine throttle for controlling its operation in response to rotation of the control lever.
U.S. Pat. No. 3,943,876, which issued to Kiekhaefer on Mar. 16, 1976, discloses a water jet boat drive that is mounted rigidly entirely outboard of the boat and driven from an inboard engine by an interconnected shaft through the transom. The tail nozzle is mounted concentric of and spaced from the pump chamber of the jet and extends rearwardly therefrom axially thereof. A butterfly trim vane is pivotally mounted on a transverse horizontal axis in the tail nozzle and is adapted to close the nozzle for blocking the jet and compelling a reverse flow of the water from the pump through the passages between the pump chamber and tail nozzle. A steering vane is mounted on a vertical axis rearwardly of the tail nozzle and carries a rudder disposed beneath the jet steering vane for steering during reversal of the jet. The engine exhaust is introduced to the jet stream within the tail nozzle and has a by-pass operable during reverse of the jet stream.
U.S. Pat. No. 4,056,073, which issued to Dashew et al on Nov. 1, 1977, describes a boat thruster that includes a diverter valve with an inlet connected to a water pump, a pair of outlets extending to either side of the boat, a valve mechanism for accurately controlling the amount of thrust obtained from both outlets, and a deflector positioned at each outlet. Each deflector is movable between a first position wherein it allows a sideward water discharge to thrust the bow to the side, and a second position wherein it directs water rearwardly to move the boat in a forward direction, or if required, to a third position to move the boat rearwardly.
U.S. Pat. No. 5,154,650, which issued to Nakase on Oct. 13, 1992, describes a water jet propulsion unit for a small watercraft that incorporates a mechanism for actuating the reverse thrust bucket through an intermediate lever so as to permit a flexible cable to be employed that lies closely above the jet propulsion unit. The actuating device is constructed so as to provide self-locking of the reverse thrust bucket in at least one of its positions. Various linkage arrangements for achieving the interrelationship are disclosed.
U.S. Pat. No. 5,755,601, which issued to Jones on May 26, 1998, discloses a brake system for a personal watercraft. The watercraft has a brake which the driver of the watercraft can use to decelerate forward motion of the watercraft. The brake mechanism preferably includes a reverse gate that allows watercraft steering to be consistent when the watercraft is accelerating or cruising with a reverse gate in a full-up position as when the watercraft is decelerating with the reverse gate in a full-down or partial-down position. The positioning of the reverse gate during the operation of the watercraft is adjusted in accordance with the state of hand operated actuators for a forward throttle control mechanism and a brake control mechanism. Preferably, an electronic controller receives a signal from the control mechanisms and outputs a control signal that directs a servomotor to move a reverse gate control cable or linkage to position the reverse gate. Forward thrust can be increased by proportionally closing the actuator for the forward thrust control mechanism. In addition, reverse thrust or braking thrust can be increased by proportionally closing the actuator for the brake control mechanism.
U.S. Pat. No. 4,315,749, which issued to Baker et al on Feb. 16, 1982, describes a non-jamming reversible jet nozzle. The reversible hydrojet boat drive for the substantially nonturbulent nozzling of water during the forward mode is disclosed and effective non-jamming seal function during the reverse mode is included. It comprises an exact nozzle continuation of the exit passage of the pump, particularly the top wall thereof, and the compatible eccentric relation of the surrounding seals of the reverse gate centered below the axis of gate rotation, thereby avoiding jamming and elevating strain on the control system.
U.S. Pat. No. 5,752,864, which issued to Jones et al on May 19, 1998, discloses a reverse gate for a personal watercraft. The reverse mechanism includes a reverse gate that provides low restriction to the flow of water through the jet pump and also provides significant steering characteristics. The reverse gate has a deflector surface with a vertical jet divide that divides the deflector surface. Both sides of the deflector surface are in the form of a simple curve. In the preferred embodiment, the simply curved deflector surfaces slant inward towards a central apex which serves as the vertical jet divide. The deflector surface spans between a starboard side support structure and a port side support structure which are pivotally mounted along a horizontal axis so that the reverse gate can be moved between a full-up position and a full-down position rearward of the jet pump. Both the starboard side support structure and the port side support structure include apertures therethrough which allow a portion of the jet flow to exit laterally from the reverse gate. When the reverse gate is in the fully down position, a portion of the jet flow is redirected forward to provide reverse thrust, and a portion of the jet of water is deflected laterally to port and laterally to starboard proportionally in accordance with the direction of the jet pump rudder.
U.S. Pat. No. 5,277,631, which issued to Henmi on Jan. 11, 1994, describes a vane arrangement for a water jet propulsion assembly. A water jet propulsion assembly for a jet ski-type watercraft includes an annular duct including a first section within which an impeller is located, a second section having a group of sloping vane members extending radially therethrough and a third section formed with a group of straight vane members extending partially radially inwardly from the inside surface of the outermost duct wall. The duct terminates in a nozzle for expelling water flowing therethrough. The second section of the duct includes radially inner and outer wall portions and the inner portion has a cap member secured to a rear end thereof. The cap member extends into the third duct section and is formed with another group of straight vane member which extend radially outwardly. The vane members function to convert the swirling water flow created by the impeller into a linear flow that is directed through the nozzle. The sloping and straight vane members are divided to permit more efficient molding of the vane sections by die casting.
When a jet propulsion system is installed in a watercraft, such as a jet boat, personal watercraft (PWC), or a jet ski, the thrust vector resulting from the ejection of water through the nozzle of the propulsion system, when the steering mechanism is centered, may not always be perfectly parallel to the centerline of the watercraft. Small variations in the manufacturing of the propulsion system and the assembly of the propulsion systems watercraft may result in a slight misalignment between the centerline of the watercraft and the thrust vector when the steering mechanism is in its center position. This will result in a slight pulling, either toward port or starboard, when the operator of the watercraft is attempting to steer the watercraft in a straight line. As a result, the operator must exert a corrective force on the steering mechanism (e.g. the steering wheel or handle bars) in order to maintain a straight course. This effect can result in operator fatigue and, in certain circumstances, create an unsafe condition.
Other factors can cause this type of steering misalignment. For example, certain watercraft exhibit different resistances to air flow on the port and starboard sides of the vessel. In other words, with a steering wheel and console located at the starboard side of the watercraft, wind resistance can cause a force against the driver's console of sufficient magnitude to create a clockwise torque on the watercraft.
Regardless of the specific source of the misalignment, it would be significantly beneficial if a means could be provided which corrects this slight misalignment and allows the operator to drive in a straight ahead course without having to exert a torque on the steering mechanism.